1. Field of the Invention
The present invention relates to a hydraulic actuator used for various mechanisms of a hydraulic type tire press, and a hydraulic system for a tire curing press for supplying pressure oil to a hydraulic control valve.
2. Description of the Related Art
A press frame of a tire vulcanizer (a tire press) comprises, as shown in FIG. 3, an upper frame 31, a lower frame 32, and a side frame 33, and a metal mold 35 is secured to the lower frame 32 through a lower mold mounting member 34. An upper metal mold 36 is secured to an upper mold mounting member 37, and is closable with respect to the lower metal mold 35. A piston rod 38 is secured to the mounting member 37, the mounting member 37 being moved up and down along a vertically elevating guide 39 by operation of an elevating cylinder 26. A pressurizing and transmitting rod 40 is stood upright on the mounting member 37, and a clamping cylinder 27 for transmitting a pressurizing force to the pressurizing and transmitting rod 40 is fixedly mounted on the upper frame 31.
The tire vulcanizer repeats the inserting step for inserting a green tire prior to vulcanization between the upper and lower metal molds 35 and 36 to close the upper and lower metal molds 35 and 36, the vulcanizing step for loading the clamping force to the upper and lower metal molds 35 and 36 so that the tire is not forced out during vulcanization to vulcanize the tire, and the taking out step for opening the mold in order to take out the vulcanized tire to vulcanize the tires sequentially. As shown in FIG. 5, the inserting step and the taking out step are referred to as xe2x80x9cdry cyclexe2x80x9d, and the step for loading the clamping force to vulcanize the tire is referred to as xe2x80x9cvulcanizing cyclexe2x80x9d. That is, the operating cycle of the tire vulcanizer is divided broadly into the dry cycle and the vulcanizing cycle.
The conventional hydraulic unit in the tire curing press is generally designed so that as shown in FIG. 4, a large capacity, 100 l/min, variable capacity pump 43 with cut-off pressure set to 125 kgf/cm2, and a large capacity, 170 l/min, fixed capacity pump 44 are respectively driven by a 22 kw motor to supply pressure oil to five presses 48 to 52. An unload valve 45 having 140 kgf/cm2 of set pressure is connected to the variable pump 43, and an unload valve 46 having 100 kgf/cm2 of set pressure is connected to the fixed pump 44. These unload valves 45 and 46 have a relief function for protecting line pressure, and a role for compensating for operating pressure of the press, and are designed so that pressure oil discharged from the pumps is switched to the press sides 48 to 52 and the tank side 53. In the conventional hydraulic unit 47, in the press closing operation during the dry cycle, pressure oil is supplied to the press sides 48 to 52 by the variable pump 43 and the fixed pump 44; and during the vulcanization, necessary flow rate is supplied to the presses 48 to 52 sides merely by the variable pump 43 to compensate for pressure. The dry cycle in the presses is approximately 1/10 of the vulcanizing cycle, and the variable pump 43 is continuously operated in order to compensate for pressure.
The variable pump 43 is always in the on-load state during the dry cycle and during the vulcanization as well, and pressure oil discharged from the pump 43 is supplied to the presses 48 to 52 sides. However, during the vulcanization, pressure oil is merely necessary for the clamping cylinder and a part of actuators such as a clamp portion, and the flow rate necessary for the presses 48 to 52 sides is lessened as a whole. Therefore, the discharge flow rate of the variable pump 43 is automatically adjusted to the minimum discharge flow rate to supply pressure oil.
However, since the variable pump always supplies pressure oil to the press sides, pressure is always applied to hydraulic lines on the press sides after the hydraulic pump to cause a leakage of the about 5 to 10 l/min mark from the hydraulic valve. Further, the flow rate necessary for the presses is variable as shown in FIG. 5, and the constant flow rate is not always necessary, and therefore, the fixed pump is in the unload state during the vulcanization, and the discharged pressure oil is thrown into the tank. As described above, in the conventional hydraulic system, the motor of the hydraulic unit is continuously operated despite the fact that the most machineries stop during the vulcanization so that two pumps are being operated without stopping. Further, since the leakage from the hydraulic valve is incontinent, there poses a problem in that power (energy) is used wastefully so that consuming electric power of the hydraulic unit is wasted.
It is an object of the present invention to provide a hydraulic system for a tire curing press for limiting operation of a hydraulic unit during vulcanization by which machineries are stopped.
The present invention provides a hydraulic system for a tire vulcanizer in which various hydraulic cylinders of a tire vulcanizer for vulcanizing and molding tires and a hydraulic unit for supplying pressure oil having a fixed pressure are connected by hydraulic lines, comprising the one or more tire vulcanizers operated by said various hydraulic cylinders, a hydraulic unit for supplying pressure oil of fixed pressure, an accumulator circuit for supplying the accumulated pressure oil to said various hydraulic cylinders, and check means provided every said tire vulcanizer so that during vulcanization of said tire vulcanizer, pressure oil of said hydraulic unit and said accumulator circuit is cut off, and in the operation of said tire vulcanizer, the cutting off is released to cause the pressure oil of said hydraulic unit and said accumulator circuit to pass.
In this case, during the dry cycle, pressure oil is supplied from the hydraulic unit and the accumulator; and during the vulcanization, a master valve constituting the check means is closed to cut off a supply of pressure oil from the accumulator and the hydraulic unit to the various hydraulic cylinders. The hydraulic unit supplies pressure oil to the accumulator to accumulate it during the time pressure oil is cut of a supply to the various hydraulic cylinders. Thereby, pressure oil can be supplied at a stretch from the hydraulic unit and the accumulator to the various cylinders during the dry cycle, and a pump having a smaller capacity than that of conventional pumps without delaying the dry cycle time for about 1 to 2 minutes. When a supply of pressure oil from the hydraulic unit and the accumulator is cut off by the master valve constituting the check means, it is not necessary to always supply pressure oil of fixed quantity in order to compensate for a leakage from the hydraulic valve in each vulcanizer but a supply quantity of pressure oil during the vulcanization can be reduced, thus enabling reduction of consuming electric power of the hydraulic unit.
The present invention further provides, in addition to the above-described constitution, a hydraulic system in which every said tire vulcanizer is provided an auxiliary accumulator for accumulating the remainder of the discharged flow rate of said hydraulic unit, if the discharged flow rate of said hydraulic unit and said main accumulator exceeds the necessary flow rate of said tire vulcanizer, to compensate for pressure of said various hydraulic cylinders during the vulcanization.
In this case, since pressure oil can be supplied to clamps or the like requiring pressure oil during vulcanization by the auxiliary accumulator without throwing out the remainder of the discharged flow rate of the hydraulic unit as in prior art, and therefore, the effective utilization of pressure oil can be achieved, and the consuming electric power of the hydraulic unit can be further reduced.
Further, according to the present invention, in addition to the above-described constitution, the hydraulic unit turns on and off a supply of pressure oil with fixed pressure of the hydraulic line being a reference.
In this case, when the hydraulic line reaches fixed pressure, the hydraulic unit is stopped, and pressure oil can be supplied merely by the main accumulator, whereby the hydraulic unit need not be operated always during the vulcanization, and the consuming power of the hydraulic unit can be further reduced.
Furthermore, according to the present invention, in addition to the above-described constitution, a supply of pressure oil and the operation of the pump are turned on and off with whether or not the tire vulcanizer is in the vulcanizing operation state being a reference, whereby pressure oil more than as needed is not supplied, and the consuming power of the hydraulic unit can be further reduced.